In many instances, it is necessary or desirable to attach an element such as a patch, threaded screw, or other structure onto a supporting substrate. For example, it may necessary to apply a thin patch to the skin of an aircraft or to the hull of a boat to repair a hole therein. Alternately, it may be desirable to mount a threaded stud or other device onto a substrate, for example, the windshield of an automobile, without requiring a hole to be made in the substrate. In many such cases, it is necessary for the attachment member to be located on the substrate with relatively high precision and further that a positive force be applied urging the attachment member against the substrate for at least some minimum time period to allow, for example, curing of an adhesive bonding agent such as a curable epoxy or the like to achieve a substantially optimized and secure bond with the substrate.
In the past, many different clamp and fixture devices have been proposed for use in temporarily holding an attachment member on the surface of a substrate during the cure time of a bonding agent. The majority of such clamp and fixture devices have required some form of mechanical connection to the substrate by means of screws or other mechanical fasteners, clamping jaws, etc. However, these devices are not suited for use with extended surface areas or for use with fragile or thin-walled substrates within which surface interruptions to accommodate mechanical fasteners are not possible or desirable. Other fixturing devices have been proposed which rely upon suction cups for holding an attachment member in position on a substrate, but suction cup devices are limited to use with relatively clean and smooth-surfaced substrates and further function to retain the attachment member in place without exerting significant positive forces urging the attachment member against the substrate. As a result, with suction cup devices, the bonding agent on the substrate can be unevenly distributed and/or cure with less than optimum bond strength.
Improved adhesive attachment devices are described and claimed in U.S. Pat. Nos. 4,302,492; 4,338,151; 4,390,546; 4,668,546; 4,778,702; and 4,822,656. More particularly, these devices disclose attachment devices having a support fixture for temporary securement to the substrate by means of a pressure sensitive adhesive or the like, in combination with force bias or spring means for applying a force urging the attachment member into positive bearing engagement with the substrate for the cure time duration of a selected adhesive bonding agent. The support fixture or a portion thereof is movable between a first position with the adhesive member substantially out of bearing engagement with the substrate to a second position with the attachment member pressed firmly against the substrate. An over-center mechanism constitutes the movable element in most of the described embodiments. Following curing of the adhesive bonding agent, the support fixture is removed from the substrate to leave the attachment member such as a threaded bolt or the like securely bonded to the substrate. In this regard, the pressure sensitive adhesive has a sufficient adhesion strength for retaining the attachment member in position during curing of the bonding agent, but insufficient adhesion strength to preclude subsequent tear-off removal of the support fixture from the substrate.
Copending U.S. Ser. No. 10/219,707, filed Aug. 14, 2002 (based on U.S. Provisional Appln. No. 60/312,691, filed Aug. 14, 2001), discloses additional adhesive attachment configurations, wherein removal of a support fixture component following curing of the adhesive bonding agent is not required. Some of the embodiments shown and described in this copending provisional application are particularly suited for adhesively mounting an attachment member to a concrete substrate which, in some instances, can present a substrate surface that is relatively rough and porous, and may be disrupted by the presence of dust and dirt particles. In a substrate surface having these characteristics, specialized adhesive bonding agents of a heat-curable type may be desirable in order to achieve a high strength bond connection. Similarly, installation of these adhesive attachment devices onto a substrate during cold weather conditions can result in a prolonged bonding agent cure time and/or a less than optimum bond strength connection, whereby relatively rapid heat curing of the bonding agent is such conditions is also desirable.
The present invention provides an improved adhesive attachment assembly which incorporates a heat source for applying heat energy in a controlled manner to an adhesive bonding agent. The present invention may thus be used with heat activated and/or heat curable bonding agents to achieve a relatively rapid and high strength bond connection with a concrete substrate or the like, and also to achieve a relatively rapid and high strength curing of a bonding agent despite cold weather conditions.
In accordance with the invention, an improved adhesive attachment assembly is provided for securely mounting an attachment member such as a threaded stud or the like relative to the surface of a substrate. The adhesive attachment assembly comprises a first attachment component defining a base surface for receiving a selected bonding agent thereon, and movably carrying a second attachment component including means for temporary attachment or securement to the substrate. Upon pressed mounting of the first attachment component with the bonding agent thereon onto the surface of the substrate, the second attachment component is movable into temporary connection with the substrate. A spring member reacting between the first and second attachment components applies a positive force urging the first attachment component against the substrate for the duration of the bonding agent cure time. A heat source is carried by the attachment assembly for applying heat energy to the bonding agent, for purposes of activating and/or rapidly curing the bonding agent to provide a substantially optimized bond strength connection between the first attachment component and the substrate.
In one preferred form, the first attachment component comprises a base fixture in the shape of a centrally dished disk to define a shallow cavity at a blind side thereof, and wherein this shallow cavity is circumscribed by the base surface of generally annular shape. The second attachment component comprises a threaded bolt or the like having an enlarged head seated within said disk cavity and a threaded shank protruding through a central disk port to a front side of the base fixture. A bolt shoulder of noncircular or square cross section or the like may be positioned within the disk port which may have a mating noncircular or square cross sectional shape or the like to prevent relative rotation between the attachment component and the base fixture. The temporary attachment means may comprise a pointed tip nail or the like such as a concrete nail for temporary connection with a concrete substrate or the like, and the spring member may comprise a leaf spring or the like reacting between the threaded bolt and the base fixture.
Alternately, the temporary attachment means may comprise a pressure sensitive adhesive member such as a pressure sensitive elastomer of the type marketed by 3M Company of Minneapolis, Minn., under the product designation VHB Type 4910 having elastomeric bulk properties allowing 100% elongation without tearing and having a coating of high strength acrylic pressure sensitive adhesive on opposite sides of the approximately 0.040 inch thick tape. This adhesive member additionally provides the spring member reacting between the threaded bolt and the base fixture. In a further alternative form, the temporary attachment means may comprise a rupturable bead or ampoule containing a selected adhesive material such as a cyanoacrylate adhesive.
The selected adhesive bonding agent is applied to the annular base surface at the blind or underside of the base fixture, wherein this bonding agent may be applied to the base surface in flowable form, or alternately in the form of a heat activated disk adhered to the base surface. The base fixture is then press-mounted onto the substrate at a selected location, followed by displacement of the threaded bolt into temporary connection with the substrate. In this configuration, the spring member applies a positive force urging the base fixture against the substrate.
The heat source carried by the attachment assembly comprises, in one preferred form, an electrical resistance heating element positioned within the bonding agent, or alternately mounted on the base fixture at a front side thereof for delivery of heat energy through a heat conductive base fixture to the bonding agent. When a heat activated bonding agent is used, this heating element may be embedded directly within the adhesive disk. The heat source is coupled to a suitable power supply, such as a battery power supply, for delivering heat energy to the bonding agent. Control means are desirably provided for cycling the delivery of heat energy in a pulsating manner.
In an alternative preferred form, the heat source may comprise a pyrogenic source in the form of an oxidizer and polymer embedded within a support disk. In one configuration, the support disk may comprise the selected bonding agent in heat activated form for mounting onto the base surface. In another configuration, the support disk may be adapted for mounting onto a front side of the base fixture to deliver heat through a heat conductive base fixture to the bonding agent. In either case, the embedded oxidizer can be ignited to produce an exothermic reaction for delivering heat energy to the bonding agent.
Other features and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.